the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jun 2025
Long term monitoring of the geoelectric field in the UK – 2012–2024
Abstract. During severe geomagnetic storms, rapid changes in the Earth’s magnetic field can induce a significant geoelectric field in the conductive subsurface. This field can cause large potential differences in grounded systems that have long conductors between earthing points, such as power lines, and cause currents to flow between them. These currents are known as Geomagnetically Induced Currents (GIC). To predict the effects on ground-based infrastructure from geomagnetic storms during space weather events, estimates of the subsurface electrical resistivity are required. These can be constructed using transfer functions between the magnetic and electric field, calculated from measurements made at short-term monitoring installations, recording for days to weeks. However, longer-term monitoring of years to decades is valuable too, as this provides a large and rich set of data encompassing both quiet periods and storms that can be used to enhance and ground-truth geoelectric field and GIC estimates. There are a limited number of permanent monitoring systems around the world, and until 2012 there were none in the UK aside from historical measurements made in the 19th century. The British Geological Survey (BGS) installed three geoelectric field monitoring sites in 2012 and 2013 co-located with our INTERMAGNET observatories at Hartland Point, Eskdalemuir and Lerwick to provide new data sets. We describe in detail how the systems were installed, their history, the electronics used to condition and digitize the signal, and how the data are processed and supplied in near real time to users. During more than a decade of measurements, we encountered several operational issues requiring mitigation and developed improvements as we gained experience of the systems.
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Status: closed
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RC1: 'Comment on egusphere-2025-2463', István Lemperger, 08 Jul 2025
-
AC1: 'Reply on RC1', Robert Lyon, 17 Jul 2025
Dear Istvan,
Thank you for your thoughtful and useful feedback on our paper. Everything you've mentioned makes sense to improve the paper and we will implement these recommendations prior to final submission. We would like to release our schematics as open hardware, however we need to discuss this with our IPR team to ensure that we do this within policy. I will raise that with them to see if it can be included with the paper or hosted in an accessible location.
Regards,
Robert Lyon on behalf of the paper authors.
Citation: https://doi.org/10.5194/egusphere-2025-2463-AC1 -
RC2: 'Reply on AC1', István Lemperger, 17 Jul 2025
Dear Robert,
thank you for your positive reply. I understand that you have to discuss about publishing the specific schematics and it is not a critical problem if it is not possible. It was just a recommendation.
Best regards,
Istvan
Citation: https://doi.org/10.5194/egusphere-2025-2463-RC2 -
AC3: 'Reply on RC2', Robert Lyon, 01 Aug 2025
Good afternoon Istvan,
Further to discussion with my co-authors, with respect to the impact of the ESK probe misalignment on the data, we are going to add a short section of additional discussion covering what we believe the effects of the misalignment to storm response and tidal analysis are within the bounds of the preliminary analysis that we have done. Because of the long distance from the sea to the ESK site, we do not believe there to be a significant impact on the tidal studies based on our current analysis. However, for storm responses we believe that the effect will vary depending on the direction of the electric field induced by the magnetic activity. The misalignment will have minimal (around 2%) impact on the magnitude of the NS e-field signal captured, so for storms with a strong NS field component but a weak EW field component the effect will be minimal. However, as the field direction becomes more EW dominant, the greater the effect of the cross-coupled field (around 21% of the EW magnitude) on the NS data, to the point where for a weak NS, strong EW storm the cross coupling may be dominant. As noted in the discussion section we have plans to run a LEMI MT system in the correct orientation alongside the static system and then to move the NS probe to the correct location. This will give us more data to base a firmer quantified conclusion on the effects of the misalignment as part of our future work.
Robert Lyon
Citation: https://doi.org/10.5194/egusphere-2025-2463-AC3
-
AC3: 'Reply on RC2', Robert Lyon, 01 Aug 2025
-
RC2: 'Reply on AC1', István Lemperger, 17 Jul 2025
-
CC1: 'Reply on RC1', Orsi Baillie, 01 Aug 2025
In response to comment regarding line 428, the authors refer to the analyses carried out by Baillie (2000) where the notation O1 is used to definethe Lunar diurnal tide caused by the Moon's gravitational pull, with a period of 25.82 hours. Following frequency analyses of the geoelectric time series, O1 was identified in the e-field data.
Citation: https://doi.org/10.5194/egusphere-2025-2463-CC1
-
AC1: 'Reply on RC1', Robert Lyon, 17 Jul 2025
-
RC3: 'Comment on egusphere-2025-2463', Anonymous Referee #2, 22 Jul 2025
The submitted manuscript describes the history of the BGS geoelectric field monitoring system development. It provides a detailed description of the system configuration at each of the three observation sites, the electronic components used for signal digitisation, and the associated data processing. Furthermore, the manuscript provides an in-depth discussion of the challenges in the geoelectric field monitoring, the sources of noise affecting the data, and applications of geoelectric field measurements.
The manuscript is significant and convincing. It is well-written and logically organised, figures and tables are appropriate. I recommend to accept the paper in its current form with two very minor corrections:
- In the Introduction: please, use either "GIC" or "GICs". You first use "GIC" abbreviation: "Geomagnetically Induced Currents (GIC)". You can continue using "GIC" hereinafter.
- Instead of the "ESA Space Weather portal", you can use the official name "ESA Space Weather Service Network" and provide the link: https://swe.ssa.esa.int
Citation: https://doi.org/10.5194/egusphere-2025-2463-RC3 -
AC2: 'Reply on RC3', Robert Lyon, 30 Jul 2025
Thank you very much for your comments and your recommended corrections. I agree with these changes and will make them in the final revision.
Citation: https://doi.org/10.5194/egusphere-2025-2463-AC2
Status: closed
-
RC1: 'Comment on egusphere-2025-2463', István Lemperger, 08 Jul 2025
Long term monitoring of the geoelectric field in the UK – 2012-2024
Robert Lyon1, Gemma S. Richardson1, Orsi Baillie1
1British Geological Survey, Research Ave South, Riccarton, EH14 4AP Edinburgh, UK
Correspondence to: Robert Lyon (rlyon@bgs.ac.uk)
Reviewer Report
General Comment: Overall, the paper presents the site selection, design, installation, and ongoing development of geoelectric observation systems installed in 2012–2013 at three remote locations: Hartland Point, Eskdalemuir, and Lerwick. These sites were co-located with INTERMAGNET observatories and chosen to be as far as possible from anthropogenic noise sources. The development of the systems was primarily driven by the need to adapt to changes observed in the data series, to address typical failures, and to mitigate challenges arising from local anthropogenic influences.
The paper provides sufficient detail on the problems encountered and the solutions implemented, thereby demonstrating the practical difficulties of operating a permanent geoelectric monitoring system with high accuracy. It discusses aspects such as digitization, site-specific filtering of the data, and the real-time transmission of processed datasets to users and to the ESA Space Weather Portal.
In my opinion, the work described in the paper constitutes a valuable contribution to our understanding of geomagnetic induction and the coupling of space weather effects into the Earth system via induction processes. The resulting dataset fills a significant gap in the field. The team has done a thorough and careful job to extract the highest quality, low-noise, and drift-free geoelectric time series from the potential differences measured between electrode pairs at the three sites. They have found appropriate responses to the challenges encountered and have produced a dataset that will be instrumental in improving the modeling of geomagnetically induced currents (GICs) during space weather events.
Section-by-Section Review:
Chapter 1 provides a clear overview of the motivation and scientific background for installing permanent geoelectric observation stations. The authors emphasize the importance of long-term monitoring of the geomagnetic field, both for capturing long-term trends and short-term variations. The chapter also includes a brief list of the very few existing permanent geoelectric observation sites worldwide, underlining the uniqueness and value of the presented work.
Section 2.1 introduces the environmental and scientific considerations that guided site selection and installation. The practical choices regarding electrode geometry and materials are well justified, especially given the spatial limitations at each observation site.
Sections 2.2 to 2.3.3 provide an authentic and thorough account of the key considerations in designing and implementing geoelectric field measurements. The paper outlines the challenges encountered during installation and operation, and how these were anticipated or resolved over the course of ten years of operational experience. The authors describe the digitization process, potential sources of offset, and the iterative development of effective lightning protection systems, along with advances in multistage amplification techniques. Site-specific anthropogenic noise filtering is shown to be a critical aspect of geoelectric monitoring, requiring carefully considered trade-offs. These decisions are well illustrated with practical examples from the field.
Chapter 3 draws attention to the typical challenges of detecting natural geoelectric signals, many of which are familiar from our own experience at the Széchenyi István Geophysical Observatory (SzIGO). These include various anthropogenic noise sources, instrumental drift, and leakage currents — such as those originating from DC railways or the grounding systems of nearby buildings. Step-like disturbances, which are notoriously difficult to filter out automatically, are also discussed. The authors highlight how periodic interferences are often tied to nearby local sources, varying by site, and not always easy to identify. At the LER site, they successfully investigated and identified most interference sources and applied appropriate filtering techniques.
Of particular interest is the observation of strong tidal signals at the HAD station — a phenomenon we do not observe at inland stations such as NCK. The paper also covers the signatures of distant lightning strikes and the effect of precipitation-induced drift in telluric field measurements. Section 3.2.3 clearly demonstrates how precipitation can influence geoelectric measurements if electrodes are not buried deep enough. At the Nagycenk station, for example, 1 m² lead plate electrodes are buried more than 2 meters below the surface. Despite this, some seasonal variation can still be observed, although the electrodes are installed on a hilltop.
Chapter 4 provides an overview of the scientific applications and research directions enabled by this unique and valuable time series of permanent telluric observations. The data's accessibility via the ESA Space Weather Portal and the BGS Geomagnetism Portal further enhances its value for the wider research community.
Comments:
The HUN-REN Research Institute of Earth Physics and Space Science (and its predecessor institutions: MTA GGKI, MTA GGI MTA CSFK GGI, ELKH GGI) has operated a permanent telluric observation system at the Széchenyi István Geophysical Observatory in Nagycenk, Hungary, since 1956. This was the first geophysical measurement system established at the observatory, later supplemented by geomagnetic observations in 1957. The original electrode spacing was 500 meters in both the north–south and east–west directions, determined to match the sensitivity of the galvanometers available at the time. However, the system often operated in saturation during at least moderately disturbed intervals due to the lack of automatic range switching.
A new telluric monitoring system, developed by the Space Research Laboratory of the Budapest University of Technology and Economics, is currently being tested at the Nagycenk observatory. It operates with a 40 Hz sampling rate, filtered to an effective 10 Hz, and features dual-range recording: when the higher-resolution (narrow-range) channel saturates, the system automatically switches to a lower-resolution (extended-range) mode. This new system has been in operation with a 250-meter electrode spacing since 2023. Similar solution to the same problem, as it is introduced in the paper under review in 2.3.2 subsection.
Review based on the provided aspects:
1. Relevance to GI
Yes, the paper addresses scientifically relevant questions within the scope of Geoscientific Instrumentation, Methods and Data Systems (GI). It focuses on long-term geoelectric monitoring, hardware development, and operational challenges—central to GI’s objectives.
2. Novelty
The paper presents several novel aspects:
-
Over a decade of operational data from co-located geomagnetic and geoelectric sensors in the UK, previously non-existent.
-
Iterative hardware developments specifically designed for geoelectric monitoring.
-
Practical field lessons in lightning protection and anthropogenic noise mitigation.
-
Insights into natural geoelectric signatures such as tidal effects and their site-specific variation.
3. Conclusions
Substantial conclusions are reached, particularly regarding:
-
The feasibility and value of long-term monitoring.
-
Engineering trade-offs for sensor robustness.
-
Data utility for both space weather and Earth system science.
4. Methods and Assumptions
Yes. The technical descriptions (e.g., amplifier noise, ADC specs, filtering strategies, lightning modeling) are thorough. Assumptions—such as regarding signal frequency bands or tidal coupling—are realistic and explicitly discussed.
5. Support for Interpretations
Yes, the presented results are sufficient to support interpretations. The use of spectral density plots, case studies (e.g., May 2024 storm, tidal signals at HAD), and historical comparisons reinforce the validity of conclusions.
6. Reproducibility
Yes. The system's design, installation procedures, electronics schematics (described in text), and filtering/data acquisition pipelines are all detailed enough for reproduction, with some site-specific exceptions (e.g., terrain constraints).
7. Credit to Related Work
Yes. The authors cite key foundational and recent works in the field, such as Boteler (2019), Love et al. (2018), and regional studies (e.g., Ádám et al., 2009; Blum et al., 2017). They clearly distinguish their original contributions, especially hardware/system design and long-term UK data generation.
8. Title Appropriateness
Yes, the title accurately and succinctly reflects the content.
9. Abstract Clarity
Yes. The abstract is concise and informative. It defines the scope, significance, instrumentation, and goals clearly.
10. Presentation Quality
The structure is logical: introduction, system description, challenges, outputs, discussion, and conclusions. Figures are well-integrated and informative. The evolution of the system over time is clearly tracked.
11. Language
Generally fluent and precise.
12. Mathematical Clarity
Yes. Formulae (e.g., thermal noise via Nyquist) are used correctly and well contextualized. Units are consistent and appropriate throughout.
13. Content Streamlining
Minor suggestion: Figures 6–11 are crucial, but the narrative could benefit from grouping the spectral analysis figures (Figures 7–8, 10–11) into composite panels for compactness. Just a recommendation.
14. References
Yes. References are numerous, up-to-date, and include most key papers in the domain. The authors appropriately cite both foundational and niche studies relevant to their work.
15. Supplementary Material
There is no mention of separate supplementary materials. However, the description of data availability (e.g., via ESA space weather portal) is sufficient for transparency. Providing links to design schematics or PCB layouts in supplemental material might further enhance reproducibility.
Recommendation
I recommend minor revisions before acceptance. The paper is an excellent and much-needed contribution to the field of geoelectric monitoring and instrumentation. Its long-term perspective, detailed hardware development, and integration into broader space weather networks are especially commendable.
1. Clarifications or Expansions Recommended
1.1. Cross-Talk Due to Misalignment at ESK
-
Issue: The paper mentions a ~12° misalignment at ESK leading to ~20% cross-coupling (Section 5), but stops short of quantifying its impact on the long-term dataset.
-
Suggestion: Include a rough estimate or preliminary analysis of how much this misalignment might bias tidal studies or storm response data.
1.2. Filter Design Parameters
-
Issue: The filtering is critical in dealing with anthropogenic noise, but only the type (low-pass, 5 Hz) is mentioned.
-
Suggestion: Please add the filter order (e.g., Butterworth, Bessel?) and analog vs digital implementation details. This improves reproducibility and transparency for others aiming to replicate the design.
2. Small Technical or Editorial Corrections Typographical / Stylistic Issues
-
“In areas where one electrode becomes waterlogged this can cause...” → insert a comma after “waterlogged”.
-
A few places use “this required mitigation” repeatedly. Vary phrasing or tighten wording (e.g., “mitigated by…”).
-
In line 428, you mention O1 — could this be a typo? Should it perhaps be M1?
-
In kine 471: Locationthat
3. Possibly Missing Aspects Worth Mentioning
3.1. Instrument Calibration and Inter-site Consistency
-
Missing: The paper does not state how consistency between sites was validated after each hardware upgrade.
-
Suggestion: Add a sentence about whether cross-calibration or inter-site comparison (e.g., response to shared storms) was done to ensure uniformity in measurements.
3.2. Power Backup or Data Gaps
-
Missing: No mention of backup power, data loss handling, or system uptime statistics.
-
Suggestion: One sentence on whether power outages caused downtime or how data continuity is ensured (e.g., battery backup, local buffering) would close this small gap.
Istvan Lemperger
-
AC1: 'Reply on RC1', Robert Lyon, 17 Jul 2025
Dear Istvan,
Thank you for your thoughtful and useful feedback on our paper. Everything you've mentioned makes sense to improve the paper and we will implement these recommendations prior to final submission. We would like to release our schematics as open hardware, however we need to discuss this with our IPR team to ensure that we do this within policy. I will raise that with them to see if it can be included with the paper or hosted in an accessible location.
Regards,
Robert Lyon on behalf of the paper authors.
Citation: https://doi.org/10.5194/egusphere-2025-2463-AC1 -
RC2: 'Reply on AC1', István Lemperger, 17 Jul 2025
Dear Robert,
thank you for your positive reply. I understand that you have to discuss about publishing the specific schematics and it is not a critical problem if it is not possible. It was just a recommendation.
Best regards,
Istvan
Citation: https://doi.org/10.5194/egusphere-2025-2463-RC2 -
AC3: 'Reply on RC2', Robert Lyon, 01 Aug 2025
Good afternoon Istvan,
Further to discussion with my co-authors, with respect to the impact of the ESK probe misalignment on the data, we are going to add a short section of additional discussion covering what we believe the effects of the misalignment to storm response and tidal analysis are within the bounds of the preliminary analysis that we have done. Because of the long distance from the sea to the ESK site, we do not believe there to be a significant impact on the tidal studies based on our current analysis. However, for storm responses we believe that the effect will vary depending on the direction of the electric field induced by the magnetic activity. The misalignment will have minimal (around 2%) impact on the magnitude of the NS e-field signal captured, so for storms with a strong NS field component but a weak EW field component the effect will be minimal. However, as the field direction becomes more EW dominant, the greater the effect of the cross-coupled field (around 21% of the EW magnitude) on the NS data, to the point where for a weak NS, strong EW storm the cross coupling may be dominant. As noted in the discussion section we have plans to run a LEMI MT system in the correct orientation alongside the static system and then to move the NS probe to the correct location. This will give us more data to base a firmer quantified conclusion on the effects of the misalignment as part of our future work.
Robert Lyon
Citation: https://doi.org/10.5194/egusphere-2025-2463-AC3
-
AC3: 'Reply on RC2', Robert Lyon, 01 Aug 2025
-
RC2: 'Reply on AC1', István Lemperger, 17 Jul 2025
-
CC1: 'Reply on RC1', Orsi Baillie, 01 Aug 2025
In response to comment regarding line 428, the authors refer to the analyses carried out by Baillie (2000) where the notation O1 is used to definethe Lunar diurnal tide caused by the Moon's gravitational pull, with a period of 25.82 hours. Following frequency analyses of the geoelectric time series, O1 was identified in the e-field data.
Citation: https://doi.org/10.5194/egusphere-2025-2463-CC1
-
-
RC3: 'Comment on egusphere-2025-2463', Anonymous Referee #2, 22 Jul 2025
The submitted manuscript describes the history of the BGS geoelectric field monitoring system development. It provides a detailed description of the system configuration at each of the three observation sites, the electronic components used for signal digitisation, and the associated data processing. Furthermore, the manuscript provides an in-depth discussion of the challenges in the geoelectric field monitoring, the sources of noise affecting the data, and applications of geoelectric field measurements.
The manuscript is significant and convincing. It is well-written and logically organised, figures and tables are appropriate. I recommend to accept the paper in its current form with two very minor corrections:
- In the Introduction: please, use either "GIC" or "GICs". You first use "GIC" abbreviation: "Geomagnetically Induced Currents (GIC)". You can continue using "GIC" hereinafter.
- Instead of the "ESA Space Weather portal", you can use the official name "ESA Space Weather Service Network" and provide the link: https://swe.ssa.esa.int
Citation: https://doi.org/10.5194/egusphere-2025-2463-RC3 -
AC2: 'Reply on RC3', Robert Lyon, 30 Jul 2025
Thank you very much for your comments and your recommended corrections. I agree with these changes and will make them in the final revision.
Citation: https://doi.org/10.5194/egusphere-2025-2463-AC2
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- 1
Long term monitoring of the geoelectric field in the UK – 2012-2024
Robert Lyon1, Gemma S. Richardson1, Orsi Baillie1
1British Geological Survey, Research Ave South, Riccarton, EH14 4AP Edinburgh, UK
Correspondence to: Robert Lyon (rlyon@bgs.ac.uk)
Reviewer Report
General Comment: Overall, the paper presents the site selection, design, installation, and ongoing development of geoelectric observation systems installed in 2012–2013 at three remote locations: Hartland Point, Eskdalemuir, and Lerwick. These sites were co-located with INTERMAGNET observatories and chosen to be as far as possible from anthropogenic noise sources. The development of the systems was primarily driven by the need to adapt to changes observed in the data series, to address typical failures, and to mitigate challenges arising from local anthropogenic influences.
The paper provides sufficient detail on the problems encountered and the solutions implemented, thereby demonstrating the practical difficulties of operating a permanent geoelectric monitoring system with high accuracy. It discusses aspects such as digitization, site-specific filtering of the data, and the real-time transmission of processed datasets to users and to the ESA Space Weather Portal.
In my opinion, the work described in the paper constitutes a valuable contribution to our understanding of geomagnetic induction and the coupling of space weather effects into the Earth system via induction processes. The resulting dataset fills a significant gap in the field. The team has done a thorough and careful job to extract the highest quality, low-noise, and drift-free geoelectric time series from the potential differences measured between electrode pairs at the three sites. They have found appropriate responses to the challenges encountered and have produced a dataset that will be instrumental in improving the modeling of geomagnetically induced currents (GICs) during space weather events.
Section-by-Section Review:
Chapter 1 provides a clear overview of the motivation and scientific background for installing permanent geoelectric observation stations. The authors emphasize the importance of long-term monitoring of the geomagnetic field, both for capturing long-term trends and short-term variations. The chapter also includes a brief list of the very few existing permanent geoelectric observation sites worldwide, underlining the uniqueness and value of the presented work.
Section 2.1 introduces the environmental and scientific considerations that guided site selection and installation. The practical choices regarding electrode geometry and materials are well justified, especially given the spatial limitations at each observation site.
Sections 2.2 to 2.3.3 provide an authentic and thorough account of the key considerations in designing and implementing geoelectric field measurements. The paper outlines the challenges encountered during installation and operation, and how these were anticipated or resolved over the course of ten years of operational experience. The authors describe the digitization process, potential sources of offset, and the iterative development of effective lightning protection systems, along with advances in multistage amplification techniques. Site-specific anthropogenic noise filtering is shown to be a critical aspect of geoelectric monitoring, requiring carefully considered trade-offs. These decisions are well illustrated with practical examples from the field.
Chapter 3 draws attention to the typical challenges of detecting natural geoelectric signals, many of which are familiar from our own experience at the Széchenyi István Geophysical Observatory (SzIGO). These include various anthropogenic noise sources, instrumental drift, and leakage currents — such as those originating from DC railways or the grounding systems of nearby buildings. Step-like disturbances, which are notoriously difficult to filter out automatically, are also discussed. The authors highlight how periodic interferences are often tied to nearby local sources, varying by site, and not always easy to identify. At the LER site, they successfully investigated and identified most interference sources and applied appropriate filtering techniques.
Of particular interest is the observation of strong tidal signals at the HAD station — a phenomenon we do not observe at inland stations such as NCK. The paper also covers the signatures of distant lightning strikes and the effect of precipitation-induced drift in telluric field measurements. Section 3.2.3 clearly demonstrates how precipitation can influence geoelectric measurements if electrodes are not buried deep enough. At the Nagycenk station, for example, 1 m² lead plate electrodes are buried more than 2 meters below the surface. Despite this, some seasonal variation can still be observed, although the electrodes are installed on a hilltop.
Chapter 4 provides an overview of the scientific applications and research directions enabled by this unique and valuable time series of permanent telluric observations. The data's accessibility via the ESA Space Weather Portal and the BGS Geomagnetism Portal further enhances its value for the wider research community.
Comments:
The HUN-REN Research Institute of Earth Physics and Space Science (and its predecessor institutions: MTA GGKI, MTA GGI MTA CSFK GGI, ELKH GGI) has operated a permanent telluric observation system at the Széchenyi István Geophysical Observatory in Nagycenk, Hungary, since 1956. This was the first geophysical measurement system established at the observatory, later supplemented by geomagnetic observations in 1957. The original electrode spacing was 500 meters in both the north–south and east–west directions, determined to match the sensitivity of the galvanometers available at the time. However, the system often operated in saturation during at least moderately disturbed intervals due to the lack of automatic range switching.
A new telluric monitoring system, developed by the Space Research Laboratory of the Budapest University of Technology and Economics, is currently being tested at the Nagycenk observatory. It operates with a 40 Hz sampling rate, filtered to an effective 10 Hz, and features dual-range recording: when the higher-resolution (narrow-range) channel saturates, the system automatically switches to a lower-resolution (extended-range) mode. This new system has been in operation with a 250-meter electrode spacing since 2023. Similar solution to the same problem, as it is introduced in the paper under review in 2.3.2 subsection.
Review based on the provided aspects:
1. Relevance to GI
Yes, the paper addresses scientifically relevant questions within the scope of Geoscientific Instrumentation, Methods and Data Systems (GI). It focuses on long-term geoelectric monitoring, hardware development, and operational challenges—central to GI’s objectives.
2. Novelty
The paper presents several novel aspects:
Over a decade of operational data from co-located geomagnetic and geoelectric sensors in the UK, previously non-existent.
Iterative hardware developments specifically designed for geoelectric monitoring.
Practical field lessons in lightning protection and anthropogenic noise mitigation.
Insights into natural geoelectric signatures such as tidal effects and their site-specific variation.
3. Conclusions
Substantial conclusions are reached, particularly regarding:
The feasibility and value of long-term monitoring.
Engineering trade-offs for sensor robustness.
Data utility for both space weather and Earth system science.
4. Methods and Assumptions
Yes. The technical descriptions (e.g., amplifier noise, ADC specs, filtering strategies, lightning modeling) are thorough. Assumptions—such as regarding signal frequency bands or tidal coupling—are realistic and explicitly discussed.
5. Support for Interpretations
Yes, the presented results are sufficient to support interpretations. The use of spectral density plots, case studies (e.g., May 2024 storm, tidal signals at HAD), and historical comparisons reinforce the validity of conclusions.
6. Reproducibility
Yes. The system's design, installation procedures, electronics schematics (described in text), and filtering/data acquisition pipelines are all detailed enough for reproduction, with some site-specific exceptions (e.g., terrain constraints).
7. Credit to Related Work
Yes. The authors cite key foundational and recent works in the field, such as Boteler (2019), Love et al. (2018), and regional studies (e.g., Ádám et al., 2009; Blum et al., 2017). They clearly distinguish their original contributions, especially hardware/system design and long-term UK data generation.
8. Title Appropriateness
Yes, the title accurately and succinctly reflects the content.
9. Abstract Clarity
Yes. The abstract is concise and informative. It defines the scope, significance, instrumentation, and goals clearly.
10. Presentation Quality
The structure is logical: introduction, system description, challenges, outputs, discussion, and conclusions. Figures are well-integrated and informative. The evolution of the system over time is clearly tracked.
11. Language
Generally fluent and precise.
12. Mathematical Clarity
Yes. Formulae (e.g., thermal noise via Nyquist) are used correctly and well contextualized. Units are consistent and appropriate throughout.
13. Content Streamlining
Minor suggestion: Figures 6–11 are crucial, but the narrative could benefit from grouping the spectral analysis figures (Figures 7–8, 10–11) into composite panels for compactness. Just a recommendation.
14. References
Yes. References are numerous, up-to-date, and include most key papers in the domain. The authors appropriately cite both foundational and niche studies relevant to their work.
15. Supplementary Material
There is no mention of separate supplementary materials. However, the description of data availability (e.g., via ESA space weather portal) is sufficient for transparency. Providing links to design schematics or PCB layouts in supplemental material might further enhance reproducibility.
Recommendation
I recommend minor revisions before acceptance. The paper is an excellent and much-needed contribution to the field of geoelectric monitoring and instrumentation. Its long-term perspective, detailed hardware development, and integration into broader space weather networks are especially commendable.
1. Clarifications or Expansions Recommended
1.1. Cross-Talk Due to Misalignment at ESK
Issue: The paper mentions a ~12° misalignment at ESK leading to ~20% cross-coupling (Section 5), but stops short of quantifying its impact on the long-term dataset.
Suggestion: Include a rough estimate or preliminary analysis of how much this misalignment might bias tidal studies or storm response data.
1.2. Filter Design Parameters
Issue: The filtering is critical in dealing with anthropogenic noise, but only the type (low-pass, 5 Hz) is mentioned.
Suggestion: Please add the filter order (e.g., Butterworth, Bessel?) and analog vs digital implementation details. This improves reproducibility and transparency for others aiming to replicate the design.
2. Small Technical or Editorial Corrections Typographical / Stylistic Issues
“In areas where one electrode becomes waterlogged this can cause...” → insert a comma after “waterlogged”.
A few places use “this required mitigation” repeatedly. Vary phrasing or tighten wording (e.g., “mitigated by…”).
In line 428, you mention O1 — could this be a typo? Should it perhaps be M1?
In kine 471: Locationthat
3. Possibly Missing Aspects Worth Mentioning
3.1. Instrument Calibration and Inter-site Consistency
Missing: The paper does not state how consistency between sites was validated after each hardware upgrade.
Suggestion: Add a sentence about whether cross-calibration or inter-site comparison (e.g., response to shared storms) was done to ensure uniformity in measurements.
3.2. Power Backup or Data Gaps
Missing: No mention of backup power, data loss handling, or system uptime statistics.
Suggestion: One sentence on whether power outages caused downtime or how data continuity is ensured (e.g., battery backup, local buffering) would close this small gap.
Istvan Lemperger